// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_BASE_WIN_HWND_SUBCLASS_H_
#define UI_BASE_WIN_HWND_SUBCLASS_H_

#include <vector>
#include <windows.h>

#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "ui/base/ui_base_export.h"
#include "ui/base/view_prop.h"

namespace ui {

// Classes implementing this interface get the opportunity to handle and consume
// messages before they are sent to their target HWND.
class UI_BASE_EXPORT HWNDMessageFilter {
public:
    virtual ~HWNDMessageFilter();

    // A derived class overrides this method to perform filtering of the messages.
    // Return true to prevent other HWNDMessageFilter's of the target HWND and the
    // system message handler |original_wnd_proc_| from receiving the message.
    // Return false to propagate the message further to other HWNDMessageFilters
    // and eventually to |original_wnd_proc|.
    // The order in which HWNDMessageFilters are added in HWNDSubclass::AddFilter
    // determines which filter gets to see the message first (a filter added first
    // will see the message first).
    virtual bool FilterMessage(HWND hwnd,
        UINT message,
        WPARAM w_param,
        LPARAM l_param,
        LRESULT* l_result)
        = 0;
};

// An object that instance-subclasses a window. If the window has already been
// instance-subclassed, that subclassing is lost.
class UI_BASE_EXPORT HWNDSubclass {
public:
    ~HWNDSubclass();

    // Adds |filter| to the HWNDSubclass of |target|. Caller retains ownership of
    // |filter|. See the comment about the order in which filters are added in
    // HWNDMessageFilter::FilterMessage.
    static void AddFilterToTarget(HWND target, HWNDMessageFilter* filter);

    // Removes |filter| from any HWNDSubclass that has it.
    static void RemoveFilterFromAllTargets(HWNDMessageFilter* filter);

    // Returns a non-null HWNDSubclass corresponding to the HWND |target|. Creates
    // one if none exists. Retains ownership of the returned pointer.
    static HWNDSubclass* GetHwndSubclassForTarget(HWND target);

    // Adds |filter| if not already added to this HWNDSubclass. Caller retains
    // ownership of |filter|. See the comment about the order in which filters are
    // added in HWNDMessageFilter::FilterMessage.
    void AddFilter(HWNDMessageFilter* filter);

    // Removes |filter|  from this HWNDSubclass instance if present.
    void RemoveFilter(HWNDMessageFilter* filter);

    LRESULT OnWndProc(HWND hwnd, UINT message, WPARAM w_param, LPARAM l_param);

private:
    class HWNDSubclassFactory;
    friend class HWNDSubclassFactory;

    explicit HWNDSubclass(HWND target);

    HWND target_;
    std::vector<HWNDMessageFilter*> filters_;
    WNDPROC original_wnd_proc_;
    ui::ViewProp prop_;

    DISALLOW_COPY_AND_ASSIGN(HWNDSubclass);
};

} // namespace ui

#endif // UI_BASE_WIN_HWND_SUBCLASS_H_
